CVE-2021-31890 – This vulnerability in Siemens industrial contro... (How to Fix)

Q: What is the severity of CVE-2021-31890?

CVE-2021-31890 has a CVSS score of 7.5 (HIGH). This vulnerability in Siemens industrial control systems allows attackers to send specially crafted TCP packets with unchecked payload lengths. Exploitation can cause information leaks or denial-of-service conditions by manipulating network buffer memory. Affected systems include Capital Embedded AR Classic, PLUSCONTROL 1st Gen, and SIMOTICS CONNECT 400 devices.

📋 TL;DR

This vulnerability in Siemens industrial control systems allows attackers to send specially crafted TCP packets with unchecked payload lengths. Exploitation can cause information leaks or denial-of-service conditions by manipulating network buffer memory. Affected systems include Capital Embedded AR Classic, PLUSCONTROL 1st Gen, and SIMOTICS CONNECT 400 devices.

💻 Affected Systems

Products:

Capital Embedded AR Classic 431-422
Capital Embedded AR Classic R20-11
PLUSCONTROL 1st Gen
SIMOTICS CONNECT 400

Versions: All versions for some products, specific versions for others (see vendor advisories)

Operating Systems: Embedded/Industrial Control Systems

Default Config Vulnerable: ⚠️ Yes

Notes: Affects multiple Siemens industrial products with different version requirements. Check specific product advisories for exact affected versions.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system crash leading to industrial process disruption, potential memory corruption enabling information disclosure, and extended downtime requiring physical intervention.

🟠

Likely Case

Denial-of-service causing temporary unavailability of affected industrial devices, potentially disrupting automated processes until manual restart.

🟢

If Mitigated

Minimal impact with proper network segmentation and monitoring, though vulnerable systems remain at risk if exposed.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires network access but no authentication. Attack complexity is low as it involves sending malformed TCP packets.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: V2303 for Capital Embedded AR Classic R20-11, V0.5.0.0/V1.0.0.0 for SIMOTICS CONNECT 400

Vendor Advisory: https://cert-portal.siemens.com/productcert/html/ssa-044112.html

Restart Required: Yes

Instructions:

1. Identify affected product and version. 2. Download appropriate firmware update from Siemens support portal. 3. Apply update following Siemens documentation. 4. Restart device. 5. Verify update success.

🔧 Temporary Workarounds

Network Segmentation

all

Isolate affected devices in dedicated network segments with strict firewall rules

Traffic Filtering

all

Implement network filtering to block malformed TCP packets at perimeter

🧯 If You Can't Patch

Implement strict network access controls to limit exposure to trusted sources only
Monitor network traffic for abnormal TCP packet patterns and implement intrusion detection

🔍 How to Verify

Check if Vulnerable:

Check device firmware version against vendor advisories. Use Siemens diagnostic tools if available.

Check Version:

Device-specific commands vary by product. Consult Siemens documentation for version checking procedures.

Verify Fix Applied:

Confirm firmware version matches patched versions listed in vendor advisories. Test network connectivity and functionality.

📡 Detection & Monitoring

Log Indicators:

Unexpected device restarts
Network connection failures
Memory allocation errors in system logs

Network Indicators:

Abnormal TCP packet sizes
Flood of malformed packets to industrial devices
Unusual traffic patterns to/from affected ports

SIEM Query:

source_ip=* AND dest_ip=[industrial_device_ip] AND (tcp.length > [normal_threshold] OR tcp.flags.malformed=true)

📊 Metadata

CVE ID: CVE-2021-31890

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-240

Published: November 9, 2021

Last Updated: November 21, 2024

🔗 References

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